1. Field of the Invention
The invention relates to a method of transmitting n-bit information words by means of code signals. The invention also relates to an information transmission system for carrying our the method, comprising a transmitting apparatus for converting n-bit information words into code signals and for transmitting the code signals via a transmission channel or transmission medium, and a receiving apparatus for reconverting the code signals into n-bit information words.
The invention further relates to a transmitting apparatus and a receiving apparatus for use in the transmission system.
2. Prior Art
Such a method, transmission system, and transmitting and receiving apparatus for the transmission of digitised audio information via an optically readable disc are known inter alia from the Applicant's British Patent Specification No. 2,083,322 (PHQ 80.007). By means of the method described therein information words representing a sampled audio signal are EFM encoded and are transmitted in EFM-encoded form. In this way an audio signal of very high quality is transmitted in a very reliable manner, provided that the bandwidth required for transmission, which is approximately 1.2 MHZ, is adequate. However, if this bandwidth decreases below the said value, and number of detection errors during the reception of the EFM-encoded signal increases very rapidly. For example, in the case of a bandwidth reduction to approximately 80% of the required bandwidth, the number of detection errors becomes so large that information transmission becomes impossible. This abrupt failure of information transfer in the case of bandwidth reduction is inherent in the current methods of transmitting digital information. Another undesired property, which is also inherent in the known methods of transmitting digital information, is the absence of flexibility of the digital format. Once a digital information transmission system has been designed, it is substantially impossible to change the quality of the transmitted information signal in a manner compatible with the predetermined format. Thus, once a standard has been selected for a digital format, it is not possible to profit from subsequent improvements in technology which would enable the quality of the transmitted signal to be improved.
Moreover, with the known digital transmission system it is also impossible to reduce the bandwidth at the expense of a lower quality of information transmission.